1. Technical Field
The present invention relates to a disk drive for playing or driving an information-recording disk, such as a magnetic disk.
2. Related Art
Although the hard disk drives (HDDs) have now being spread as external storage units for personal computers, price reduction has put forwarded as their record density increases. In the recent, there has been an advent of home-use electronic products having built-in HDDs. The HDDs are capable of storing video and music contents in quantity and hence the products utilizing them are placed into marketing one after another. It is expected to mount them upon the car audio products. The DVDs nowadays are in the mainstream in the field of car navigation systems. It is however expected of shift from now on into HDDs.
The basic structure of an HDD is shown in FIG. 1. The HDD adopts a ramp-loading scheme that a float head slider 51 arranged at a tip of the actuator 54 is mechanically floated from a surface of the magnetic disk.
As shown in the figure, the magnetic head 51 on the actuator 54 is arranged for radial movement (shown by arrows) of the magnetic disk 53 and positioned by a voice coil motor (VCM) 160. Although the magnetic head 51 is urged onto the surface of the magnetic disk 53 by an elastic force of the suspension 57, it is controlled to have a distance of several tens of μm to the disk surface of the magnetic disk 53 due to aerodynamic floating force acting upon the magnetic head 51 by a rotation of the magnetic disk 53. Meanwhile, the magnetic head 51 not in operation is positioned in a retracted position where it is on a taper 56 of a ramp 55 formed at one end of the housing frame 50.
FIG. 2 shows a positional relationship in a sectional view between the magnetic head 51 and the ramp 55. As shown in the figure, the ramp 55 positioned close to the outer periphery of the magnetic disk 53 has a taper 56 given gradually higher than a surface of the magnetic disk 53 in a direction toward a radial outward of the disk. When reading information from or writing information to the magnetic disk 53 (i.e. in driving), the magnetic head 51 positions at a play position (in a position a) with a proper spacing to a main surface of the magnetic disk 53. In out of operation (or in unload), it gets over the taper 56 as shown by the arrow A to reach a retract position, or home position b, for waiting.
In the meanwhile, the foregoing HDD is given a function called emergency unload. The emergency unload function refers to a function that, where power voltage to the motor for driving the spindle 52 and magnetic head 51 is greatly decreased, the head 51 is forcibly moved to the retract position, in order to prevent a magnetic disk 53 from being damaged by the magnetic head 53. A power supply is required for carrying out the emergency unload. There is known an arrangement that, when the both power supplies fail, the emergency unloading is performed by the use of a reverse electromotive force, i.e. no-load electromotive force, caused by the inertial rotation of the spindle motor 52.
When the above-mentioned disk drive apparatus is used as a disk drive apparatus mounted on an engine-driven vehicle, a battery voltage greatly decreases at a startup of the engine and accordingly the emergency unload operation as the foregoing will be effected each time the engine is started up.
FIG. 3 shows an example of a power supply circuit in an engine-driven vehicle. That is, an alternator G is driven by an engine, not shown. The alternating current supplied from the alternator G is rectified and smoothed by a rectifier D and then supplied to a battery B. The battery voltage Vb on the battery B is supplied to a movable contact m of an engine-key switch SW. The engine key switch SW has fixed terminals ACC, ON and ST. The battery voltage Vb passed through the terminal ACC is supplied as ACC power to a light load such as an audio unit. The battery voltage Vb passed through the terminal ON is supplied as ON power to a heavy load HL such as a power window actuator. The battery voltage Vb passed through the terminal ST is supplied as an MST voltage to a starter motor (not shown), to rotate the starter motor and start up the engine. On the other hand, the battery voltage Vb is supplied as a backup power to a light load LL through a line BU.
FIGS. 4A and 4B show voltage on the power supply lines how the voltages of BACKUP and ACC change at the engine start. FIG. 4A depicts a manner of change in power voltage of the backup power supply while FIG. 4B depicts a manner of change in the ACC power supply. Meanwhile, the timings (I), (II), (III) and (IV) respectively correspond to the key switch positions of the engine key. (I) represents a case the engine key is positioned at an ACC position to supply power to a light load such as an audio unit, (II) a case at an ON position to supply power to a heavy load, for example, of the power window actuator or the like, (III) a case at an ST position to supply power to the starter motor and (IV) a case the engine key is returned to the ON position
During such engine start operations, there is a possibility that the backup power voltage decreases due to drop in the battery voltage. (period (III) (IV) in FIGS. 4A and 4B.)
Accordingly, where the HDD is mounted on an engine-driven vehicle, there is a high possibility that such emergency unload operation as mentioned above occur each time the engine is started up due to the drop in the power voltage because of the great amount of power consumption by the starter motor. Because the emergency unload is to forcibly move the head by utilizing the reverse electromotive force of the spindle motor as described above, there are increased occasions in the vehicular-mounted disk drive that the float head slider 51 collide with the taper 56 on the ramp 55 in the course of reaching the wait position b on the ramp 55 as compared to the case where the disk drive is mounted on a home-use device such as a home-use personal computer. In other words, the vehicular-mounted HDD requires increased endurance for the magnetic head 51. This circumstance is commonly problematic for the disk drive apparatuses for use with unstable power voltage.